Add .env.example file for environment variable configuration

- Created a new `.env.example` file to outline required environment variables for the application, including database and messaging service credentials.

Author: toreleon

.env.example

@@ -0,0 +1,14 @@
+SECRET_KEY=
+ALGORITHM=
+ACCESS_TOKEN_EXPIRE_MINUTES=
+MONGO_DATABASE_NAME=
+MONGO_USERNAME=
+MONGO_PASSWORD=
+MONGO_HOST=
+MONGO_PORT=
+REDIS_URL=
+RABBITMQ_HOST=
+RABBITMQ_PORT=
+RABBITMQ_USERNAME=
+RABBITMQ_PASSWORD=
+RABBITMQ_VHOST=